Gmail MCP Server

A remote FastMCP server for sending Gmail messages through a single owner Gmail identity. The server is designed for Prefect Horizon and relies on Horizon's gateway authentication for MCP access.

Features

• Horizon-managed MCP authentication

• Server-owned Gmail refresh token for the owner Gmail identity

• Gmail send, draft creation, draft listing, and draft sending tools

• Professional email composition prompts, resources, and helper tools

• Remote-only Horizon entry point at main.py:mcp

Deployment

Deploy this repository to Prefect Horizon from the default branch.

Configure Horizon with:

• Entrypoint: main.py:mcp

• Horizon authentication: enabled

Set these deployment environment variables:

• GOOGLE_OAUTH_CLIENT_ID: Google OAuth client ID for the owner Gmail token

• GOOGLE_OAUTH_CLIENT_SECRET: Google OAuth client secret for the owner Gmail token

• GOOGLE_OAUTH_REFRESH_TOKEN: refresh token for the owner Gmail identity

• ALLOWED_GMAIL_EMAIL: the Gmail address the refresh token must belong to

The Google OAuth refresh token must include these scopes:

https://www.googleapis.com/auth/gmail.send
https://www.googleapis.com/auth/gmail.modify

Horizon controls who may connect to the MCP server. The backend uses the configured owner Gmail refresh token for Gmail API calls.

Local Verification

Install dependencies:

uv sync

Inspect the Horizon entry point with dummy local configuration:

GOOGLE_OAUTH_CLIENT_ID=test.apps.googleusercontent.com \
GOOGLE_OAUTH_CLIENT_SECRET=test \
GOOGLE_OAUTH_REFRESH_TOKEN=test-refresh-token \
ALLOWED_GMAIL_EMAIL=owner@example.com \
uv run fastmcp inspect main.py:mcp

For a real local OAuth test, copy the example environment file and fill in your Google OAuth web client values:

cp .env.example .env

Then load it before running the local HTTP server:

set -a
source .env
set +a
uv run fastmcp run main.py:mcp --transport http --host 127.0.0.1 --port 8000

Run quality checks:

uv run ruff check .
uv run pytest

Available MCP Tools

Core Gmail Tools

• send_email: send an email immediately

• create_draft: create an email draft

• send_draft: send an existing Gmail draft

• list_drafts: list Gmail drafts

• get_user_info: return the authenticated Gmail profile

Email Assistance Tools

• get_subject_line_help

• validate_subject_line_tool

• get_email_templates

MCP Prompts

• professional_email_composer

• follow_up_email_generator

• meeting_request_composer

• draft_strategy_advisor

• email_review_checklist

MCP Resources

Template resources are exposed for professional HTML emails, signatures, and email guidelines.